1. Field of the Invention
The present application relates to light emitting devices using light emitting diode(s) to generate lights of desired color(s).
2. Background of the Invention
With the development of efficient LED devices that emit bluish or ultraviolet (UV) light, it has become feasible to produce LED devices that generate white light through phosphor conversion of a portion of the primary radiation emission of the light emitting structure of the LED device to longer wavelengths. Conversion of primary emission to longer wavelengths is commonly referred to as down-conversion of the primary emission. An unconverted portion of the primary emission combines with the light of longer wavelength to produce white light. LED devices that produce white light through phosphor conversion are useful for signaling and illumination purposes.
Recent developments have been focused on the phosphor materials to improve the production of white lights by using LED devices. See, for example, U.S. Pat. No. 5,998,925 entitled “Light emitting device having a nitride compound semiconductor and a phosphor containing a garnet fluorescent material” filed by Shimizu et al on Jul. 29, 1997; U.S. Pat. No. 6,501,102 entitled “Light emitting diode (LED) device that produces white light by performing phosphor conversion on all of the primary radiation emitted by the light emitting structure of the LED device” filed by Mueller-Mach et al on Aug. 28, 2001; U.S. Pat. No. 6,642,652 entitled “Phosphor-converted light emitting device” filed by Collins, III et al on Jun. 11, 2001; U.S. Pat. No. 6,686,691 entitled “Tri-color, white light LED lamps” filed by Mueller et al on Sep. 27, 1999; U.S. Pat. No. 6,812,500 entitled “Light-radiating semiconductor component with a luminescence conversion element” filed by Reeh et al on Dec. 6, 2000.
However, as stated in the SCIENTIFIC AMERICAN article, titled “In Pursuit of the Ultimate Lamp”, published in the February 2001 issue, the use of phosphor material in the production of white light is “inherently less efficient, because energy is lost in converting ultraviolet or blue light into lower-energy light (that is, light toward the red end of the spectrum). Moreover, light is also lost because of scattering and absorption in the phosphor packaging.” (Page 67).
There have been few discussions about reduction of energy consumptions in the production of white color light. The conventional use of phosphors in the production of white color light may even result in higher energy consumption.